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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4410
Maxim > Design Support > Technical Documents > Application Notes > Battery Management > APP 4410
Maxim > Design Support > Technical Documents > Application Notes > Circuit Protection > APP 4410
Keywords: battery backup, diode-OR, comparators, voltage references
APPLICATION NOTE 4410
Battery Backup with Delay
By: Robert Nicoletti, Applications Engineer
Jul 28, 2009
Abstract: This application note explains that the simplest link from a main supply and backup battery to a
load is the diode-OR connection. However simple that concept, a diode-OR does not work when the
battery voltage exceeds the main supply voltage. The article presents a circuit which handles that
condition. The MAX931 comparator with 2% reference is featured in the design.
This design idea appeared in the May 25, 2006 issue of Electronic Design magazine.
The simplest link from a main supply and backup battery to a load is the diode-OR connection. However,
a diode-OR does not work when the battery voltage exceeds the main supply voltage. The Figure 1
circuit handles that condition. The main switch-mode supply voltage ranges from 7V to 30V, and the
backup supply is a 9V battery.
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